If you have this gene, you will definitely get Alzheimer's. Would you want to know?

Gina Kolata

Marty and Matt Reiswig, two brothers in Denver, knew that Alzheimer's disease ran in their family, but neither of them understood why. Then a cousin, Gary Reiswig, whom they barely knew, wrote a book about their family, The Thousand Mile Stare.

Marty and Matthew Reiswig have a family history of carrying a genetic mutation that causes early-onset Alzheimer's. Matthew has chosen to be tested, but Marty has not. Photo: Nick Cote/New York Times

In the extended Reiswig family, Alzheimer's disease is not just a random occurrence. It results from a mutated gene that is passed down from parent to child.

If you inherit the mutated gene, Alzheimer's will emerge at around age 50 - with absolute certainty. Your child has a 50-50 chance of suffering the same fate.

The revelation came as a shock. And so did the next one: The brothers learned that there is a blood test that can reveal whether one carries the mutated gene. They could decide to know if they had it. Or not.

It's a dilemma more people are facing as scientists discover more genetic mutations linked to diseases. Often the newly discovered gene increases risk, but does not guarantee it.

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Sometimes knowing can be useful: If you have a gene mutation that makes colon cancer much more likely, for example, then frequent colonoscopies may help doctors stave off trouble.

But then there are genes that make a dreaded disease a certainty: There is no way to prevent it, and no way to treat it.

Marty Reiswig, 37, saw his father, now in the final stages of Alzheimer's, slowly lose his ability to think, to remember, to care for himself, or even to recognise his wife and sons.

Reiswig knows that if he has the gene, he has perhaps a bit more than a decade before the first symptoms appear. If he has it, his two young children may have it, too.

He wavers about getting tested.

"Sometimes I think, 'This is a terrible storm on the horizon that could absolutely devastate us, and I want to know if it is real or not.' Other times I say, 'Gosh, if I do find out that it is real and I know I will die that way and I know probably the age I will die - that is an almost unbearable amount of information about my future'."

"People say you could go sky diving or ride a bull. But you can only do things like that as long as time and income provide. You still have to get up in the morning and go to work and pay your bills."

He joined a study at the Washington University School of Medicine in St Louis in which researchers are following members of families with the genes for early-onset Alzheimer's disease. At a recent meeting, he recalled, he found himself in a room full of people like himself: All had a parent with an Alzheimer's gene.

All were at risk of having the mutated gene themselves.

Reiswig asked the group, "How many have been tested?"

Half raised their hands.

"Of those of you who have been tested, how many regret it?"

He was met with ominous silence.

Then a man spoke up. He said he had been tested and learned he has the gene.

As for regrets, "it depends on the day," the man said. "I have battled weight issues and the suicide issue, and I have had problems with my marriage ever since I found out. Some days I really regret it. It is a huge burden. Other days I am glad I know."

Reiswig has been thinking it over. He has decided not to be tested.

"For me, the return is not worth the investment," he said.

His 41-year-old brother Matt, who lives nearby with his wife and five children, was plagued by the fear that he had the mutated gene. Every time he lost his keys or forgot a name, he thought: Alzheimer's.

"I was already living every single day, every single moment assuming I had it," he said. "I did not want to find out I have it. I wanted to find out I don't have it."

He decided to have the test.

"To me, it is just so obvious," he said. "Worrying about what the truth is, is far more damaging, and it doesn't change the conclusions."

Knowing the truth, he added, "frees you from making the wrong assumptions".

Matt Reiswig got lucky. He does not have the gene. He wept when he got the news, thinking of all the time and energy he had spent thinking he had it. All the emotional heartache.

His cousin Brian Whitney, 43, was not as fortunate.

His father has the gene and has Alzheimer's. When he was 40, Whitney, decided to have the test, telling himself that he had to know for the sake of his family, and especially his tro-year-old daughter.

Would she have to watch him start to lose his memory when she was just 10? Would she have to see him die? Might he have passed the gene on to her?

If he had the gene, he told himself, he would volunteer for research studies; he would do anything he could to help scientists understand the disease and treat it, if not for his sake then for his daughter's.

Whitney's test came back positive. He has the gene. He thought he was prepared, but nothing really prepares a person to hear such news.

On good days, he almost manages to forget about what is coming; on bad days, it is all he thinks about. He's entered a clinical trial: A nurse comes to his house each month to inject him with an experimental drug. It has become a monthly reminder of the future.

Friends have said to him that they cannot understand why he put himself through the torture of knowing, not to mention getting a drug that might make matters worse, for all anyone knows.

"I shake my head and say: 'You have no idea what you are talking about. My only control is being involved in research. Live my life and have my family history before you judge me.'"